Laser module

Abstract

The laser module includes a QCL element, a diffraction grating unit including a movable diffraction grating, a first lens that transmits light emitted from an end surface of the QCL element and light returning from the movable diffraction grating to the QCL element, a second lens that transmits terahertz waves emitted from the QCL element, a first holder, and a package. The first holder has a support surface on which the QCL element is mounted and a side surface connected to the support surface and facing the first lens in a resonance direction. A distance from an intersection point between the side surface and the support surface to the end surface along the resonance direction is smaller than a distance between the intersection point and the first lens along the resonance direction.

What is claimed is: 
     
         1 . A laser module comprising:
 a quantum cascade laser that includes:
 a substrate having a main surface and a back surface opposite to the main surface; 
 a first clad layer provided on the main surface; 
 an active layer provided on an opposite side of the first clad layer to the substrate; and 
 a second clad layer provided on an opposite side of the active layer to the first clad layer, 
 wherein the active layer has a first end surface and a second end surface facing each other in a second direction orthogonal to a first direction that corresponds to a stacking direction of the substrate, the first clad layer, the active layer, and the second clad layer, 
 the first end surface constitutes a resonator for oscillating light of a first frequency and light of a second frequency, and 
 the active layer generates a terahertz wave having a difference frequency between the first frequency and the second frequency; 
   a diffraction grating unit that includes a movable diffraction grating constituting an external resonator for the light of the first frequency;   a first lens disposed between the quantum cascade laser element and the movable diffraction grating and configured to transmit light emitted from the second end surface and light returning from the movable diffraction grating to the quantum cascade laser element; and   a second lens disposed at a position facing the first end surface and configured to transmit the terahertz wave emitted from the quantum cascade laser element;   a first holder configured to hold the quantum cascade laser element; and   a package that accommodates the quantum cascade laser element, the diffraction grating unit, the first lens, and the first holder and in which an optical path between a light incident surface of the second lens and the movable diffraction grating is disposed,   wherein the first holder includes:
 a support surface on which the quantum cascade laser element is mounted; 
 a first side surface connected to the support surface and facing the first lens in the second direction, and 
   when viewed from a direction orthogonal to the first direction and the second direction, a first distance from an intersection point between the first side surface and the support surface to the second end surface along the second direction when a direction from the first lens toward the quantum cascade laser element along the second direction is a positive direction is smaller than a second distance between the intersection point and the first lens along the second direction.   
     
     
         2 . The laser module according to  claim 1 , wherein the first distance is less than or equal to 0. 
     
     
         3 . The laser module according to  claim 1 , wherein the first distance is 0. 
     
     
         4 . The laser module according to  claim 1 , wherein
 a resonance axis passing through the first end surface and the second end surface in the quantum cascade laser element intersects an optical axis of the second lens by the support surface being inclined such that the support surface intersects the optical axis of the second lens, and   the first end surface is spaced apart from the light incident surface of the second lens.   
     
     
         5 . The laser module according to  claim 1 , wherein the first lens and the diffraction grating unit are fixed to the first holder. 
     
     
         6 . The laser module according to  claim 1 , wherein the second lens is a hemispherical or super-hemispherical silicon lens. 
     
     
         7 . The laser module according to  claim 1 , wherein
 the first holder has a second side surface connected to the support surface and facing the second lens in the second direction, and   the first end surface is located closer to the second lens than the second side surface in the second direction.   
     
     
         8 . The laser module according to  claim 1 , wherein
 the package has a side wall facing the first end surface,   the side wall has a through hole penetrating in a third direction perpendicular to the side wall,   the through hole includes:
 a first hole portion that opens to an inside of the package; 
 a second hole portion that opens to an outside of the package, and that includes the first hole portion and is larger than the first hole portion when viewed from the third direction; and 
 an annular counterbore surface connecting the first hole portion and the second hole portion and extending along a plane intersecting the third direction, and 
   an outer edge portion of the light incident surface of the second lens is inserted into the second hole portion from the outside of the package and is fixed in surface contact with the counterbore surface.   
     
     
         9 . The laser module according to  claim 8 , wherein the first end surface is located inside the first hole portion. 
     
     
         10 . The laser module according to  claim 9 ,
 wherein the first holder includes:
 a main body portion that includes a portion located closer to the first lens in the support surface and the first side surface; and 
 a protruding portion connected to the main body portion and including a portion located closer to the second lens in the support surface, and 
   at least a portion of the protruding portion is located inside the first hole portion.   
     
     
         11 . The laser module according to  claim 1 , further comprising a second holder configured to hold the second lens, wherein
 the second lens and the second holder are accommodated in the package,   the package has a side wall facing the first end surface, and   the side wall is provided with a light exit window for transmitting light that is emitted from the first end surface and passes through the second lens.   
     
     
         12 . The laser module according to  claim 11 , wherein the second holder is fixed to the package independently of the first holder. 
     
     
         13 . The laser module according to  claim 11 , wherein
 the first lens and the diffraction grating unit are fixed to the first holder, and   the second holder is integrally formed with the first holder or is fixed to the first holder.   
     
     
         14 . The laser module according to  claim 11 , wherein
 the second holder has a through hole penetrating in a third direction perpendicular to the side wall,   the through hole includes:
 a first hole portion that opens toward the quantum cascade laser element; and 
 a second hole portion that opens toward the side wall, and that includes the first hole portion and is larger than the first hole portion when viewed from the third direction; and 
 an annular counterbore surface connecting the first hole portion and the second hole portion and extending along a plane intersecting the second direction, and 
   an outer edge portion of the light incident surface of the second lens is inserted into the second hole portion from a side wall side and is fixed in surface contact with the counterbore surface.   
     
     
         15 . The laser module according to  claim 14 , wherein the first end surface is located inside the first hole portion. 
     
     
         16 . The laser module according to  claim 15 ,
 wherein the first holder includes:
 a main body portion that includes a portion located closer to the first lens in the support surface and the first side surface; and 
 a protruding portion connected to the main body portion and including a portion located closer to the second lens in the support surface, and 
   at least a portion of the protruding portion is located inside the first hole portion.   
     
     
         17 . The laser module according to  claim 10 , wherein
 a width of the protruding portion in a fourth direction orthogonal to the first direction and the second direction is smaller than a width of the main body portion in the third direction.   
     
     
         18 . The laser module according to  claim 16 , wherein
 a width of the protruding portion in a fourth direction orthogonal to the first direction and the second direction is smaller than a width of the main body portion in the third direction.   
     
     
         19 . The laser module according to  claim 17 , wherein
 the protruding portion is formed in a shape in which the width of the protruding portion gradually decreases toward the second lens along the second direction.   
     
     
         20 . The laser module according to  claim 18 , wherein
 the protruding portion is formed in a shape in which the width of the protruding portion gradually decreases toward the second lens along the second direction.